[xen stable-4.16] passthrough/x86: stop pirq iteration immediately in case of error

[patchbot@xxxxxxx]

commit 18d0f501596bd55412282aac3db1f0a349a68f50
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Tue Jan 25 13:35:23 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jan 25 13:35:23 2022 +0100

    passthrough/x86: stop pirq iteration immediately in case of error
    
    pt_pirq_iterate() will iterate in batch over all the PIRQs. The outer
    loop will bail out if 'rc' is non-zero but the inner loop will continue.
    
    This means 'rc' will get clobbered and we may miss any errors (such as
    -ERESTART in the case of the callback pci_clean_dpci_irq()).
    
    This is CVE-2022-23035 / XSA-395.
    
    Fixes: c24536b636f2 ("replace d->nr_pirqs sized arrays with radix tree")
    Fixes: f6dd295381f4 ("dpci: replace tasklet with softirq")
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    master commit: 9480a1a519cf016623f657dc544cb372a82b5708
    master date: 2022-01-25 13:27:02 +0100
---
 xen/drivers/passthrough/x86/hvm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/xen/drivers/passthrough/x86/hvm.c 
b/xen/drivers/passthrough/x86/hvm.c
index 351daafdc9..0b37cd145b 100644
--- a/xen/drivers/passthrough/x86/hvm.c
+++ b/xen/drivers/passthrough/x86/hvm.c
@@ -732,7 +732,11 @@ int pt_pirq_iterate(struct domain *d,
 
             pirq = pirqs[i]->pirq;
             if ( (pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) )
+            {
                 rc = cb(d, pirq_dpci, arg);
+                if ( rc )
+                    break;
+            }
         }
     } while ( !rc && ++pirq < d->nr_pirqs && n == ARRAY_SIZE(pirqs) );
 
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